1. Field of the Invention
The present invention relates to an apparatus for and a method of applying an electromagnetic wave to a liquid, and more particularly to an apparatus for and a method of applying an electromagnetic wave such as ultraviolet rays or the like to various liquids including water being processed in wastewater treatment plants, industrial drains, water for various uses, sewage, purified water, drinking water, pure water, ultrapure water, etc.
2. Description of Related Art
The application of electromagnetic waves such as ultraviolet rays or the like to liquids is widely used for the purposes of treating or sterilizing trace amounts of contaminants by way of excitation and/or dissociation of molecular bonds of organic substances or oxidizing agents. According to such a process, ultraviolet rays and an oxidizing agent such as ozone are used together to generate OH radicals, which decompose underwater contaminants by way of oxidization. The process does not produce secondary waste materials and is capable of decomposing dioxins and so on in water.
It is customary to apply ultraviolet rays to a liquid to be treated from an ultraviolet lamp which is sealed in a watertight fashion by a transparent protective tube of quartz and immersed in a tank that contains the liquid to be treated. When the protective tube sealing the ultraviolet lamp is immersed in the liquid to be treated, inorganic substances such as metals (iron, manganese, etc.) in the liquid or organic substances in the liquid are attached to the outer circumferential surface of the transparent protective tube, depositing a covering thereon which tends to lower the radiated intensity of the ultraviolet rays.
There is known another method of treating a liquid by letting the liquid flow in the form of a thin film down a vertical wall surface and irradiating the liquid with an electromagnetic wave such as ultraviolet rays or the like emitted from a position spaced from the liquid. Since the source of the electromagnetic wave such as ultraviolet rays or the like is positioned remotely from the liquid, the method is effective to prevent the problem that contaminants are attached to a protective tube or the like of an electromagnetic wave source, lowering the radiated intensity. However, the distance between the electromagnetic wave source and the liquid to be treated poses a problem. Specifically, if the distance between the electromagnetic wave source and the liquid to be treated is large, then the radiated intensity of the electromagnetic wave is reduced. If the distance between the electromagnetic wave source and the liquid to be treated is reduced and the electromagnetic wave source and the liquid to be treated are positioned closely to each other, then the radiated intensity of the electromagnetic wave can be achieved, but it is difficult to form a stable, high-speed thin film of liquid flowing down a vertical wall surface. In case the amount of the liquid to be treated is small, a thin film of liquid can be formed which can sufficiently be irradiated with an electromagnetic wave. In case the amount of the liquid to be treated is large, however, the thickness of the film of liquid flowing down is increased, and when the speed of the flowing liquid is increased, the thin film of liquid becomes unstable, producing splashes which are scattered and contaminate the electromagnetic wave source.
The present invention has been made in view of the above drawbacks. It is an object of the present invention to provide an apparatus for and a method of applying an electromagnetic wave to treat a large amount of liquid stably without causing an electromagnetic wave source to be contaminated.
According to the present invention, an electromagnetic wave applying apparatus comprises an electromagnetic wave source, a cylinder surrounding the electromagnetic wave source, a liquid retention tank disposed around the cylinder, and an inlet portion for introducing a liquid overflow from the liquid retention tank as a thin film flowing down an inner wall surface of the cylinder, which is irradiated with an electromagnetic wave from the electromagnetic wave source, wherein the inlet portion has a curved surface joining an overflow portion of the liquid retention tank to the inner wall surface of the cylinder.
Since the overflow portion of the liquid retention tank and the inner wall surface of the cylinder are connected to each other by the curved surface of the inlet portion, a thin-film liquid layer can be formed stably on the inner wall surface of the cylinder even if the liquid flows in a large quantity. Consequently, the electromagnetic wave applying apparatus can increase the amount of the liquid treated thereby without contaminating the electromagnetic wave source.
The electromagnetic wave applying apparatus preferably includes swirling flow forming means for causing the liquid introduced from the inlet portion onto the inner wall surface of the cylinder to flow as a swirling flow down the inner wall surface.
According to another aspect of the present invention, an electromagnetic wave applying apparatus comprises an electromagnetic wave source, a cylinder surrounding the electromagnetic wave source, a liquid retention tank disposed around the cylinder, an inlet portion for introducing a liquid overflow from the liquid retention tank as a thin film flowing down an inner wall surface of the cylinder, which is irradiated with an electromagnetic wave from the electromagnetic wave source, and swirling flow forming means for causing the liquid introduced from the inlet portion onto the inner wall surface of the cylinder to flow as a swirling flow down the inner wall surface.
Even when the liquid splashes, since the direction of the liquid splashes is tangential to the inner wall surface of the cylinder, the protective tube disposed at the center of the cylinder is prevented from being contaminated by liquid splashes. The liquid flowing down the inner wall surface of the cylinder is subject to centrifugal forces, producing the thin film of the liquid uniformly and stably.
The inner wall surface of the cylinder is preferably slanted such that the diameter thereof is greater upwardly and smaller downwardly. With the slanted inner wall surface, the liquid is not peeled off the inner wall surface of the cylinder, and flows smoothly down the inner wall surface.
Preferably, the electromagnetic wave comprises ultraviolet rays and the electromagnetic wave source comprises an ultraviolet lamp.
According to the present invention, a method of applying an electromagnetic wave to a liquid comprises; introducing a liquid along a curved surface to an inner wall surface of a cylinder from an upper end thereof, flowing the liquid to flow as a thin film down the inner wall surface of the cylinder; and applying an electromagnetic wave from an electromagnetic wave source disposed substantially centrally in the cylinder to the liquid.
The electromagnetic wave is preferably applied to the liquid while the liquid is flowing as a swirling thin film down the inner wall surface of the cylinder from the upper end thereof.
According to another aspect of the present invention, a method of applying an electromagnetic wave to a liquid comprises; flowing a liquid to flow as a swirling thin film down an inner wall surface of a cylinder from the upper end thereof; and applying an electromagnetic wave to the liquid from an electromagnetic wave source disposed substantially centrally in the cylinder.